APOGAMOUS FERNS. EVOLUTION OF THE SEPARATE SPECIES 

 The last of the apogamous species, D. Borreri, remains, and here we have richer 

 material than in any other recorded case, since the species is not only widespread and 

 abundant in our own flora but, unhke the Beech Fern which is also abundant but more 



I 





%y. 





m 







« ^ c 



Fig. 192. Cytology of Pellaea atropurpurea (L.) Link, a. Two focal levels of mitosis in a root from 

 a section stained in gentian violet, x 1500. b. Meiosis in an eight-celled sporangium in balsam 

 after acetocarmine. x 1000. c. Meiosis in a sixteen-celled sporangium showing pairs and 

 univalents in balsam after acetocarmine. x 1000. For explanatory diagrams see Fig. 193. 



\ 



•♦ 







Pef/aea "en" --87 n--87 



Fig. 193. Explanatory diagrams to Fig. 192 a and h. x 1500. 



uniform, we have a considerable variety of different forms to examine from which some 

 genetical evidence can be obtained even in the present state of the inquiry. 



Two types of material should, in the first instance, be called to mind. On the one 

 hand, there are the host of monstrosities beloved of fern collectors of which the var. 

 polydactyla Wills and the var. polydactyla Dadds may be taken as samples, and on the 



186 



